Capacitive attenuation circuitry is commonly found in the front-end of radio frequency (RF) receivers for purposes of attenuating an input RF signal. FIG. 1 illustrates conventional variable capacitive attenuation circuitry 100 that employs multiple series capacitors CA0 and CA1-CAN that are coupled together in parallel between an RF signal input 120 and an attenuated RF signal output 130, and that also employs multiple shunt capacitors CB0 and CB1-CBN that are coupled together in parallel between series capacitors CA0 and CA1-CAN and ground. Together, the series capacitor/s CA and shunt capacitor/s CB that are active in the circuit 100 at any given time act to form a capacitive divider that attenuates an incoming RF signal applied to RF signal input 120. In some cases, series capacitors CA and/or capacitors CB may be optionally binary weighted.
As shown in FIG. 1, each of series capacitors CA0 and CA1-CAN can be removed from the in-line signal path between RF signal input 120 and attenuated RF signal output 130 by using a respective control signal (not shown) to cause opening of a respective MOS transistor switch 102, 104 or 106 so that the removed series capacitor floats, while a switch 162 is closed to apply a voltage bias 160 to each floating series capacitor to reduce nonlinearity. Similarly, each of shunt capacitors CB0 and CB1-CBN can be isolated from ground by using a respective control signal (not shown) to cause opening of a respective MOS transistor switch 108, 110 or 112 so that the isolated shunt capacitor floats, while a switch 172 is closed to apply a voltage bias 170 to each floating shunt capacitor to reduce nonlinearity. In this manner, the amount of attenuation between RF signal input 120 and attenuated RF signal output 130 can be varied by changing the combination of capacitors CA0 and CA1-CAN that are coupled in the signal path between RF signal input 120 and attenuated RF signal output 130, and by changing the combination of capacitors CB0 and CB1-CBN that are coupled to ground. In particular, variable capacitive attenuation circuitry 100 acts as a capacitive divider that attenuates an incoming RF signal applied to RF signal input 120 by an amount that is equal to the selected series capacitance divided by the sum of the selected series capacitance and the selected shunt capacitance that is coupled to ground at any given time.